A batch weighing device is well known in the prior art and generally includes a plurality of separate bins, each of which has a screw auger or the like for conveying a desired amount of each individual ingredient into a common hopper so as to create a batch of selected amounts of selected ingredients. One such typical system may include up to sixteen separate bins supported from a single framework and arranged in two banks of eight bins each, each bin weighing approximately 100 pounds and when filled weighing as much as 400-600 pounds. The common hopper is generally supported between the two banks by four load cells such that its weight may be accurately monitored and the cumulative weight of the mixture used to determine the amount of each ingredient to be added to the hopper.
These batch weighing systems may be used in applications wherein one or more of the ingredients are drugs falling under the regulation of the Food and Drug Administration (FDA). The FDA has recently issued guidelines for businesses utilizing batch weighing equipment of this design that require the operator to accurately ascertain the weight of the ingredient contained in the bin on a periodic basis. In the prior art, the amount of ingredient was determined through a volumetric reading obtained by measuring the level of ingredient in the bin against a measuring tape glued to the sidewall of the interior of the bin. However, volumetric readings have not satisfied the FDA such that weight measurements are now being required.
One solution to this in the prior art has been to removably mount the individual bins to the framework such that an overhead hoist may be used to individually lift the bins from the framework so that a digitized load cell in series with the hoist hook can measure the weight of the material contained within the bin. Not only is this method time-consuming and, hence, expensive, but it is also cumbersome to lift the bins individually from the framework and replace them. As a result, material commonly falls from the end of the bins auger which not only can result in loss of valuable ingredients, but can also result in contamination between bins of different ingredients.
An obvious solution to weighing each of the bins individually would be to support each bin by four load cells, much as is presently done with the common hopper. However, the load cells can be quite expensive. This additional expense would dramatically increase the cost of the batch weighing apparatus and therefore is not feasible as a solution to this problem.
To solve these and other problems in the prior art, and to enable the individual bins of a batch weighing apparatus to be weighed in place without their removal from the supporting framework, the inventor herein has succeeded in designing and developing a bin suspension system comprised of a plurality of flexures which, when coupled with a single load cell, can be used to accurately weigh each individual bin and its contents. Thus, only a single additional load cell is required for each bin with the result being that the continuous instantaneous weight of each bin so equipped is known.
Simply put, the plurality of flexures are used to restrict movement of the bin to substantially a vertical direction as the bin is loaded with ingredient. A single load cell is interconnected between the bin and the supporting framework and serves as substantially the only support for the bin in the vertical direction. With this arrangement, the output of the load cell thus represents the weight of the bin and its contents.
The type of flexure used can be either one of two designs as proposed herein. The first of these is essentially a turnbuckle with rod end bearings. These flexures, or links, are oriented in a horizontal plane and extend between two sides of the bin and the supporting framework. The links are oriented at angles with respect to each other in the same grouping so as to prevent tilting of the bin sideways about its vertical axis. Additionally, the links are grouped at each side, with groups for different sides lined in different horizontal planes such that the bin is permitted to tilt or cant slightly as it moves up or down. This minimizes compression and tension in the links as the bin moves and also facilitates freer movement of the bin in the vertical direction to provide greater accuracy in the weighment of the bin. Alternately, the links may be oriented into a three or four legged parallelogram extending from the inboard side of the bin to the framework. In this configuration, the movement of the bin is generally arcuate and is thought to be more vertical and, hence, more accurate.
Still another type of flexure proposed by the inventor comprises a steel bar, perhaps one inch square, with all but one-tenth of an inch drilled out along the width of the bar near each of the two connection points to provide flex joints therein. With this type of link, it is thought that a reduced number of links may be used as the flex joints formed in the steel bar have an orientation which naturally prevent flexing other than along the length dimension of the bar. Thus, separate links oriented angularly to the others need not be provided to prevent movement of the bin sideways with respect to its vertical axis.
As shown in the preferred embodiments, the load cell may be placed on the outboard side of each bin for ease in access, adjustment, and retrofit installation, if required. With this arrangement, and the arrangement of the flexures as shown, the flexures are placed in compression which is believed to detract from the accuracy of the weighment. Alternately, a platform type load cell may be placed beneath each bin at approximately its center of gravity so as to eliminate either compression or tension being placed in the flexures. While this may provide additional accuracy in measuring each weighment, the load cell is not nearly as accessible and is also more expensive. In a typical batch weighing device, each load cell has a movement between 0.005" (five thousandths of an inch) and 0.050" (fifty thousandths of an inch) to measure the difference between an empty bin and a full bin. With this small amount of movement, it is not believed that meaningful additional accuracy may be attained through use of a platform type load cell, when compared to the additional expense required. However, from a theoretical standpoint, central placement of the load cell may improve accuracy.
With the flexures and load cell of the present invention, accurate weighments of each individual bin may be made without removing the bin from the supporting framework. Furthermore, very little additional mechanical complexity is required along with only a single load cell. Therefore, continuous, on-line measurement of the weight of each ingredient is available and the shutting down of the apparatus to individually lift each bin therefrom to obtain weighments is eliminated. It is believed that this invention provides significant advantages over the prior art in meeting the FDA requirements recently imposed.
While the principal advantages and features of the invention have been noted above, a greater understanding of the invention may be attained by referring to the drawings and description of the preferred embodiment which follow.